Design Advice

[isaac]

Hi All

I have just got an email from the customer he likes the idea of using an ibutton (Doesn't want wireless?)but he still insist that he does not want the driver to get out of the cab to touch the ibutton so i am nearly back to square one.(He wants to use the line for the revease line.
i was thinking i was thinking of using an ibutton but i need to isolate the 24v that is put on the line when its in reverse somehow.
i also dont know if the 1 wire protocol can withstand noise etc.
i need some guildance on this.
i attached the schematic which i would like to use but not quite sure if this would do the job

Regards
Isaac

[Darrel Taylor]

For iButtons, you have to have a Pull-up resistor that supplies both power and the high side of the data.

I don't think the pull-up can overcome the Pull-down from the filaments of the light bulbs.
And if it could, the lights would always be partially on, and the ibutton would be dead after the first pulse trying to drive that much current.

Due to the inductance of the filaments you might be able to pass a low freq RF over that line, but probably not DC.
<br>

[isaac]

Ooops
it back to the drawing boards

[isaac]

For iButtons, you have to have a Pull-up resistor that supplies both power and the high side of the data.

I don't think the pull-up can overcome the Pull-down from the filaments of the light bulbs.
And if it could, the lights would always be partially on, and the ibutton would be dead after the first pulse trying to drive that much current.
<br>

Yes i agree with you i didn't take this into consideration

Due to the inductance of the filaments you might be able to pass a low freq RF over that line, but probably not DC.
<br>

How can i do this i am cracking up here

Regards
Isaac

[isaac]

Thanks DT

what if the circuit is modified as the attached image
using the relay contact to completely isolate the lamp from the circuit

Regards
Isaac

[Darrel Taylor]

I don't know Isaac,

It looks like the delay of the relay would still allow the iButton to take a pretty big 24V hit. I don't think the parasitic power cap in the ibutton could take too many of those.

Just thinking out loud here.

If on the cab side, the current to the reverse lights was monitored with a hall effect current sensor. And, on the trailer side a normally ON solid state relay or FET was placed in series with the light bulbs. Then the lights can be turned on and off (fast enough not to interfere with the lights being on) by a PIC sending serial data. The current sensor in the cab would pick up that signal easily for the receiving side.

Then every time you put it in reverse, the 24V will power up the PIC and it'll transmit what it's attached to. Same thing could be done with brake, turn signals or running lights.
<br>

[Archangel]

Hi Issac,
Your customers trucks are using 6 pin connectors? There are 7 pin trailer connectors available for large vehicles: http://www.accessconnect.com/images/wiring_7pole.jpg Does he now use a 7 pin with a charge line ?

[ZOOM]

I don't know Isaac,


Just thinking out loud here.

If on the cab side, the current to the reverse lights was monitored with a hall effect current sensor. And, on the trailer side a normally ON solid state relay or FET was placed in series with the light bulbs. Then the lights can be turned on and off (fast enough not to interfere with the lights being on) by a PIC sending serial data. The current sensor in the cab would pick up that signal easily for the receiving side.

Then every time you put it in reverse, the 24V will power up the PIC and it'll transmit what it's attached to. Same thing could be done with brake, turn signals or running lights.
<br>

DT
How can this be posible as the pic in the trailer to send serial data (There is only going to be the 24v line as its output.

[Darrel Taylor]

The idea is to read the Current being sent to the reverse lights from the cab. It's actually an analog output from the current sensor, but with the sensitivity cranked up ... the output will be "High" (output saturated) with any current being drawn, and "Low" when there's no current.

Then in the trailer, it turns the lights on/off via serial data to the solid state relay.

For incandescent lights, fast on/off times won't be noticed visually. May cause a little dimming, but it only takes a few milliseconds to send the data so noone will even notice.

This way it doesn't matter what the voltage is on the line. Works on 12v just as well as 24V.

[rhino]

Due to the inductance of the filaments you might be able to pass a low freq RF over that line, but probably not DC.
<br>

This sounds like a cool idea..... like X10?